Please use code tags next time, so that it's easier for us to tell you which line to work on.
On the line (whichever on it is) where you declare your compute() function, you gave it a return type of int, change it to void and you're set.

This simply means that each function takes an input of type int as parameter and returns a value of type int. You are not returning any value in your present code. If you do not want them to return anything, declare them as:

void Compute(int x);

and

void InputFunction(int x);

and while calling, you have to give them a valid int input so that these functions can process it accordingly.